Changes

|+ {{table number|1}}Summary of methods used to derive hydrocarbon reserves

|+ {{table number|1}}Summary of methods used to derive hydrocarbon reserves

|-

|-

! Method

! Method || Application || Accuracy

! Application

! Accuracy

|-

|-

| Volumetric

| Volumetric || OOIP, OGIP, recoverable reserves. Use early in life of field. || Dependent on quality of reservoir description. Reserves estimates often high because this method does not consider problems of reservoir heterogeneity.

| OOIP, OGIP, recoverable reserves. Use early in life of field.

| Dependent on quality of reservoir description. Reserves estimates often high because this method does not consider problems of reservoir heterogeneity.

|-

|-

| Material balance

| Material balance || OOIP, OGIP (assumes adequate production history available), recoverable reserves (assumes OOIP and OGIP known). Use in a mature field with abundant geological, petrophysical, and engineering data. || Highly dependent on quality of reservoir description and amount of production data available. Reserve estimates variable.

| OOIP, OGIP (assumes adequate production history available), recoverable reserves (assumes OOIP and OGIP known). Use in a mature field with abundant geological, petrophysical, and engineering data.

| Highly dependent on quality of reservoir description and amount of production data available. Reserve estimates variable.

|-

|-

| Production history

| Production history || Recoverable reserves. Use after a moderate amount of production data is available. || Dependent on amount of production history available. Reserve estimates tend to be realistic.

| Recoverable reserves. Use after a moderate amount of production data is available.

| Dependent on amount of production history available. Reserve estimates tend to be realistic.

|-

|-

| Analogy

| Analogy || OOIP, OGIP, recoverable reserves. Use early in exploration and initial field development. || Highly dependent on similarity of reservoir characteristics. Reserve estimates are often very general.

| OOIP, OGIP, recoverable reserves. Use early in exploration and initial field development.

| Highly dependent on similarity of reservoir characteristics. Reserve estimates are often very general.

|}

|}

* ø = [[porosity]] (decimal) from log and/or core data

* ø = [[porosity]] (decimal) from log and/or core data

* ''S''_w = connate water saturation (decimal) from log and/or core data

* ''S''_w = connate water saturation (decimal) from log and/or core data

* B_oi = formation volume factor for oil at initial conditions (reservoir bbl/STB) from lab data; a quick estimate is ''B''_oi = 1.05 + (''N'' × 0.05), where ''N'' is the number of hundreds of ft³ of gas produced per bbl of oil [for example, in a well with a GOR of 1000, ''B''_oi = 1.05 + (10 × 0.05)]

* B_oi = formation volume factor for oil at initial conditions (reservoir bbl/STB) from lab data; a quick estimate is <math>B_{oi} = 1.05 + (N \times 0.05)</math>, where ''N'' is the number of hundreds of ft³ of gas produced per bbl of oil [for example, in a well with a GOR of 1000, ''B''_oi = 1.05 + (10 × 0.05)]

Another basic volumetric equation is

Another basic volumetric equation is

|+ {{table number|2}}Estimation of primary recovery factor

|+ {{table number|2}}Estimation of primary recovery factor

|-

|-

!

! Drive Mechanidm || Primary Recovery Factor Drive Mechanism (%)

! Primary Recovery Factor Drive Mechanism (%)

|-

|-

| Depletion

| colspan = 2 | Depletion

|-

|-

|     Solution gas

|     Solution gas || 18–25

| 18–25

|-

|-

|     Expansion

|     Expansion || 2–5

| 2–5

|-

|-

| Gas cap drive

| Gas cap drive || 20–40

| 20–40

|-

|-

| Water drive

| colspan = 2 | Water drive

 

|-

|-

|     Bottom

|     Bottom || 20–40

| 20–40

|-

|-

|     Edge

|     Edge || 35–60

| 35–60

|-

|-

| Gravity

| [[Gravity]] || 50–70

| 50–70

|}

|}

One general equation is

One general equation is

:Change in pore volume = Change in oil volume + change in free gas volume + change in water volume

:<math>\text{Change in pore volume} = \text{ Change in oil volume } + \text{ change in free gas volume } + \text{ change in water volume}</math>

where

where

* Change in pore volume = ''NB''_oi/(1 – ''S''_wi)''c''_f''P''

* <math>\text{Change in pore volume} = \frac{NB_{oi}}{(1 - S_{wi})}c_fP</math>

* Change in oil volume = ''NB''_oi –(''N'' – ''N''_p)''B''_oi

* <math>\text{Change in oil volume} = NB_{oi} - (N - N_p)B_{oi}</math>

* Change in gas volume = (''GB''_gi – ''GB''_g) + [''N''_p''R''_p ''(N'' – ''N''_p) – NR_si]''B''_g due to gas produced, evolved, and encroached from a gas cap

* <math>\text{Change in gas volume} = (GB_{gi} - GB_g) + [N_p R_p (N - N_p) - NR_{si}] B_g</math> due to gas produced, evolved, and encroached from a gas cap

* Change in water volume = –''NB''_oi''S''_wi/(1 – S_wi)''c''_w''P'' – ''W''_e + ''W''_p''B''_w, due to connate water volume change, encroached water, and produced water

* <math>\text{Change in water volume} = \frac{-NB_{oi}S_{wi}}{(1 - S_{wi})}c_wP - W_e + W_pB_w</math>, due to connate water volume change, encroached water, and produced water

where

where

The material balance technique for calculating gas reserves, like material balance for oil, attempts to mathematically equilibrate changes in reservoir volume as a result of production. The basic equation is

The material balance technique for calculating gas reserves, like material balance for oil, attempts to mathematically equilibrate changes in reservoir volume as a result of production. The basic equation is

:Weight (or SCF) of gas produced = weight (or SCF) of gas initially in the reservoir – weight (or SCF) of gas remaining in the reservoir

:<math>\text{Weight (or SCF) of gas produced} = \text{ weight (or SCF) of gas initially in the reservoir } - \text{ weight (or SCF) of gas remaining in the reservoir}</math>

The equations used to calculate OGIP are

The equations used to calculate OGIP are

===Reservoir simulation===

===Reservoir simulation===

The material balance method is actually a subset of the mathematical techniques that are available to modern petroleum engineers. Reservoir simulators use material balance as well as fluid flow equations to model the reservoir as a group of interconnected tanks. The advent of powerful computers has made the use of numerical simulation quite common for estimating reserves and recovery as well as initial volume in place. Since reservoir simulation can account for performance history through history matching, this method incorporates facets of all the techniques discussed. With sufficient data and prudent use of simulators, this method provides the best recovery estimates for complex reservoirs.

The material balance method is actually a subset of the mathematical techniques that are available to modern [[petroleum]] engineers. Reservoir simulators use material balance as well as fluid flow equations to model the reservoir as a group of interconnected tanks. The advent of powerful computers has made the use of numerical simulation quite common for estimating reserves and recovery as well as initial volume in place. Since reservoir simulation can account for performance history through history matching, this method incorporates facets of all the techniques discussed. With sufficient data and prudent use of simulators, this method provides the best recovery estimates for complex reservoirs.

==Production history analysis==

==Production history analysis==

|+ {{table number|3}}Decline equations

|+ {{table number|3}}Decline equations

|-

|-

! Solving for

! Solving for || Exponential || Hyperbolic

! Exponential

! Hyperbolic

|-

|-

| Rate of production

| Rate of production || <math>q_t = q_{\text{i}}e^{-Dt}</math> || <math> q_{t} = q_{\rm i}(1 + nD_{\rm i}t)^{-1/n}</math>

| ''q''_t = ''q''_i ''e''^{– ''Dt''}

| ''q''_t = ''q''_i (1 + ''nD''_i ''t'' )^{–1/ ''n''}

|-

|-

| Cumulative production

| Cumulative production || <math>N_p = \frac{(q_{\text{i}} - q_t)}{D}</math> || <math> N_{\rm p} = \frac{q_{\rm i}^{n}}{[(1 - n)D_{\rm i}]}(q_{\rm i}^{1 - n} - q_{\rm t}^{1-n})</math>

| ''N_p'' = ( ''q''_i – ''q_t'' )/ ''D''

| <math> q_{t} = q_{\rm i}(1 + nD_{\rm i}t)^{-1/n}</math><br />

<math> N_{\rm p} = q_{\rm i}^{n}/[(1 - n)D_{\rm i}](q_{\rm i}^{1 - n} - q_{\rm t}^{1-n})</math><br />

<math>t = [(q_{\rm i}/q_{\rm ec})^{n} - 1/nD_{\rm i}</math>

|-

|-

| Life of reservoir

| Life of reservoir || <math>t = \left( \frac{1}{D} \right) \ln \left( \frac{q_{\text{i}}}{q_{ec}} \right)</math> || <math>t = \left( \frac{q_{\rm i}}{q_{\rm ec}} \right)^n -\frac{1}{nD_{\rm i}}</math>

| ''t'' = (1/ ''D'' )ln( ''q''_i / ''q''_ec )

| ''t'' = [( ''q''_i ''/q''_ec ) ''ⁿ'' – 1/ ''nD''_i

|}

|}

==Analogy method==

==Analogy method==

* [[Reservoir modeling for simulation purposes]]

* [[Reservoir modeling for simulation purposes]]

* [[Waterflooding]]

* [[Waterflooding]]

* [[Fundamentals of fluid flow]]

* [[Fluid flow fundamentals]]

* [[Conducting a reservoir simulation study: an overview]]

* [[Conducting a reservoir simulation study: an overview]]

* [[Introduction to reservoir engineering methods]]

* [[Introduction to reservoir engineering methods]]

* [http://archives.datapages.com/data/alt-browse/aapg-special-volumes/me10.htm Original content in Datapages]

* [http://archives.datapages.com/data/alt-browse/aapg-special-volumes/me10.htm Original content in Datapages]

* [http://store.aapg.org/detail.aspx?id=612 Find the book in the AAPG Store]

* [http://store.aapg.org/detail.aspx?id=612 Find the book in the AAPG Store]

[[Category:Reservoir engineering methods]]

[[Category:Reservoir engineering methods]]